1. Field of the Invention
The present invention relates to an imager for reading optical symbologies such as traditional bar codes and 2D symbologies. More particularly, the present invention relates to a hand-held optical code imager which quickly and easily adjusts illumination and focus and has an preferred operating range of approximately 1.5 to 16 inches, however, the imager may have an operating range with both lower and higher limits, and still fall within the intended scope of the present application.
2. Description of the Prior Art
The use of bar codes has proliferated to the point where they are used in almost every industry to provide machine readable information about an item or product and to help track such items. Numerous different symbologies have been developed, such as one dimensional linear codes and 2D codes, such as Data Matrix. Typical linear codes comprise a series of parallel lines of varying thickness and spacing which are arranged in a linear configuration to represent a digital code containing information relating to the object. The use of bar codes has expanded due to the fact that the imaging and tracking process eliminates human error and can be performed quickly.
The amount of information a bar code can contain is dependent upon the size of the markings employed in the bar code, which determines the density of the code. Linear bar codes such as UPC codes, are only recorded in one dimension. On the other hand, 2D symbologies are encoded in two dimensions to contain greater information density.
In a typical reading process, a spot of light from a laser is projected and swept across the code, and the reflected light is sensed by a photosensitive element. In conventional imagers, lasers are used as the source illumination. Scanners may be either installed in a fixed location or portable hand-held units.
Hand-held scanners must be designed to operate in situations where the number of varying factors is greater than for fixed scanners. For instance, the distance between the scanner and the bar code, the amount of illumination, the focusing of the scanner, the orientation of the scanner relative to the bar code, and the angle of the scanner relative to the bar code are all factors which must be considered for the scanner to operate correctly. For instance, U.S. Pat. No. 5,296,690 to Chandler et al. discloses a system for locating and determining the orientation of bar codes in a two-dimensional image. The Chandler et al. patent is primarily concerned with making sure that the scan of the bar code is performed correctly with regard to the orientation of the scanner and the bar code.
Some hand-held scanning devices have a wand-like configuration where the device is intended to make contact with the code as it is swept across the code. Such a wand eliminates the variation in the distance between the scanner and the code and therefore requires no focusing.
Two-dimensional arrays such as CCD arrays have been used to create the image of the bar code as it is scanned, but traditionally a laser and a single photodiode are used for scanning a linear bar code. A CCD having dimensions of 640 by 480 pixels provides sufficient resolution for use with VGA monitors, and is widely accepted. The video image is sensed in the CCD, which generates an analog signal representing the variation in intensity of the image, and an analog to digital converter puts the image signal into digital form for subsequent decoding. Two dimensional sensors are used with spatially oriented 2D codes.
For a non-contact hand-held scanner, it is necessary to be able to read the bar code over a reasonable distance, to provide sufficient illumination, to focus the scanner onto the bar code and perform the entire operation in a reasonable amount of time. While it may be possible to create an imager which can perform all of the desired functions, if the imager does not operate in a manner the user finds comfortable and sufficient, then the imager will not be accepted by end users and will not be commercially viable. For example, if the imager cannot perform the focusing quickly enough, then variations in the position of the scanner, due to the inability of the user to hold the imager steady, will create problems which cannot be easily overcome.
By way of example, if a scanner takes too long to perform a focusing function from the moment the user depresses a trigger, then the position of the scanner relative to the bar code may vary during the focusing operation thereby requiring yet another focusing operation. Similarly, such movement in the position of the scanner relative to the bar code will change the parameters for achieving the desired illumination.
Scanners which have been designed to read linear, or one dimensional, codes are, for the most part, incapable of scanning 2D symbologies. Linear and 2D symbologies may be provided on items by attaching a label to the item, putting the item in a container having a preprinted code, or by directly marking the product, such as by etching. Most conventional scanners may find it difficult to read symbologies which have been etched directly onto a product.
These and other deficiencies of the prior art are addressed by the present invention which is directed to a hand-held imager which is capable of reading both linear one dimensional codes and two dimensional symbologies, which can perform illuminating and focusing steps quickly and accurately so as to eliminate variation in the position of the imager relative to the code, and which can operate in an environment where the imager is preferably positioned anywhere from substantially 1.5 inches to 16 inches from the targeted code.
The hand-held imager of the present invention can perform omnidirectional coded symbology reading for both linear and two-dimensional symbologies over relatively long working distances. The imager includes an imaging system having a focusing system, an illumination system, and a two-dimensional photodetector which forms an image of the bar code. After achieving targeting of the coded symbology, the reader of the present invention adjusts illumination and then the focus between multiple different focuses, and utilizes a portion of the two-dimensional photodetector to determine the optimum focus. Upon the determination of optimum focus, the focusing system is configured at the optimum focusing configuration established in the initial focusing step, and an image is created using the entire two-dimensional photodetector.
A targeting system visually assists the user to position the reader so that the coded symbology, being targeted, is within the field of view of the reader. The reader has two types of illumination, one for symbologies which are close to the reader, and a second type of illumination for symbologies which are farther from the reader. The two-dimensional photodetector may be employed to determine the optimum illumination.
The proper illumination and focus are produced by utilizing a photometric analysis by developing entropy scores for each illuminating condition associated with the optical plates. The quality or nature of the transitions (peak-to-peak) are taken into account by the analysis to produce the entropy scores. Focus analysis is performed by developing entropy scores for dark field and bright field zones with the illuminating condition obtained from the previous photometric analysis. A focused image has a sharp contrast between light and dark areas. The image with the highest population density at high frequency indicates the best focus.
Unfortunately, while typical one-dimensional bar codes and certain two-dimensional symbologies can take advantage of current photometric and focus analysis techniques, direct parts marking (DMP) in which generally a two-dimensional symbology is directed attached to or etched into a machine part offers a distinct challenge to produce the correct focus and illumination for a particular scanned code. This is due to the fact that in DMP applications, the marked surfaces (from low reflection black to highly reflected shiny surfaces) and various marking techniques are quite diverse. This would create a situation in which current focus and photometric techniques can not possibly cover the majority of cases without manually changing some of the illuminating parameters, such as intensity, exposure and gain.
The illuminating parameters of intensity, exposure and gain could be modified among themselves to obtain similar pictures. For example, if the intensity is fixed, an image taken with a long exposure and low gain will be similar to an image taken with a short exposure and a high gain. Unfortunately, when using a hand-held scanner, it is important to complete the scan very quickly. Therefore, the proper focus likewise and illumination values must be determined very quickly. Consequently, it would be quite impractical, if not impossible to provide a rather long exposure to compensate for a low gain, due to the speed of optical plates rotation used to calculate the correct focus.
It is an object of the present invention to provide a hand-held reading device capable of reading both linear and 2D coded symbology.
Another object of the present invention is to provide a hand-held reader which can perform an imaging operation in a range between 1.5 inches and 16 inches to the coded symbology for typical hand-held use, but may have both higher and lower distance limits.
Yet another object of the present invention is to provide a hand-held reader capable of reading direct product markings in addition to coded symbology printed on labels.
Still another object of the present invention is to provide a hand-held reader which utilizes a two dimensional sensor to facilitate focusing and illumination adjustment.
Yet another object of the present invention is to provide a hand-held reader which utilizes a two dimensional sensor to facilitate focusing and illumination adjustment, where only a small portion of information received by the two dimensional sensor is used, to thereby speed processing.
Another object of the present invention is to provide a hand-held reader made from commonly available xe2x80x9coff-the-shelfxe2x80x9d components.
Still another object of the present invention is to provide a method of simultaneously focusing and providing the proper illumination for a two-dimensional coded symbology when the two-dimensional code is applied to a part, regardless of the composition of the part as well as the two-dimensional code.